JPH09113913A - Chiral smectic liquid crystal element and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to obtain the good and uniform orientation of oriented films formed as thin films by forming LB films of an alignment layer thickness on electrodes consisting of amorphous ITO subjected to surface flattening. SOLUTION: This chiral smectic liquid crystal element has a pair of the substrates 11a, 11b which are disposed to face each other by holding the chiral smectic liquid crystals 15 therebetween and are respectively formed with the transparent counter electrodes 12a, 12b for impressing voltage on the chiral smectic liquid crystals 15 on their opposite surfaces. The chiral smectic liquid crystals 15 in an oriented state exhibits at least two optically stable states. At least one electrodes of a pair of the counter electrodes 12a, 12b consist of the amorphous ITO subjected to surface roughening and have the alignment layers 14a, 14b consisting of the LB films having <=5nm film thickness thereon.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, a liquid crystal device used in a liquid crystal optical shutter, and the like, and more particularly to a chiral smectic liquid crystal device. More specifically, it improves display characteristics by improving the alignment state of chiral smectic liquid crystal molecules. And a chiral smectic liquid crystal device.

[0002]

2. Description of the Related Art A display device of the type in which transmitted light rays are controlled by using a refractive index anisotropy of a ferroelectric liquid crystal in combination with a polarizing element has been proposed by Clark and Lagerwall ( JP-A-56-107216, U.S. Pat. No. 4,367,924.
No. specification).

This ferroelectric liquid crystal generally has a chiral smectic C phase (SmC ^* ) or H phase (SmH ^* ) in a specific temperature range. In this state, the first liquid crystal responds to an applied electric field. Has an optical stable state and a second optical stable state, and has the property of maintaining that state when no electric field is applied, that is, bistability, and also responds to changes in the electric field. It is fast and expected to be widely used for high speed and memory type display devices.

In order for the optical modulation element using the chiral smectic liquid crystal having the bistability to exhibit predetermined element characteristics, the liquid crystal arranged between the pair of parallel substrates must be
A uniform alignment state without defects, and efficient conversion of the above two stable states due to the application of an electric field,
In addition, it is necessary that the molecular orientation is such that the previous state is maintained when no electric field is applied.

[0005]

Generally, in order to orient a chiral smectic liquid crystal, a polymer having horizontal or tilt orientation such as polyimide (PI), polyvinyl alcohol (PVA) or polyamide (PA) on the surface of a substrate. A pair of substrates, on which a film is formed and subjected to a rubbing treatment in substantially the same direction, is used. However, since the polymer alignment film between the electrode and the liquid crystal layer acts as an insulator layer, the first optically stable state (for example, white display state) and the second optically stable state (for example, black display state). When a one-polarity voltage for switching to a state) is applied, after the application of this one-polarity voltage, a reverse electric field V _{rev of the} other polarity is generated in the chiral smectic liquid crystal layer due to the presence of spontaneous polarization, and this reverse electric field V _rev is the afterimage at the time of display, or a state in which the first optical stable state (for example, white display state) and the second optical stable state (for example, black display state) cannot be switched ( It has been clarified that it causes switching failure).

It has been clarified that the switching failure due to the reverse electric field V _rev as described above can be solved by increasing the capacity of the alignment film (for example, Akio Yoshida, October 1987, "Liquid Crystal Conference Preliminary Report"). ”,“ Switching characteristics of SSFLC ”on pages 142 to 143).

Further, since the capacity of the alignment film can be increased by thinning the alignment film, the thinning of the alignment film formed on the substrate (for example, a film thickness of 5 nm or less) causes afterimages and switching failures. Therefore, it is possible to achieve a predetermined display characteristic in which bistability is maintained.

Incidentally, the Langmuir-Blodgett (LB) method is effective for thinning the alignment film, and by using this method, a uniform alignment film having a thickness of several nm or less can be formed.

On the other hand, ITO (Indium Tin Oxid) used as a transparent electrode for forming an alignment film.
Since the thin film such as e) has unevenness of about several nm on its surface, the alignment state of the liquid crystal is affected by the unevenness when the thickness of the alignment film formed on the transparent electrode is thin. Isotropic phase (Iso) without cholesteric phase (Ch)
-Smectic A phase (SmA) -When a liquid crystal having a chiral smectic phase transition is used, Iso phase-S
Since the unevenness disturbs the uniaxiality of the Batone during the mA phase transition, there arises a problem that it is difficult to obtain uniform alignment of the liquid crystal. Therefore, L is formed on the transparent electrode having such unevenness.
When the alignment film having a film thickness of about 5 nm is formed by the B method, it is difficult to obtain uniform alignment of the liquid crystal due to the influence of unevenness.

The present invention has been made in view of the above problems, and an object of the present invention is to obtain good uniform alignment with an alignment film which is thinned (for example, a film thickness of 5 nm or less) with respect to the chiral smectic liquid crystal. To do.

[0011]

The structure of the present invention to achieve the above object is as follows.

That is, the first aspect of the present invention is to provide a pair of substrates, which are opposed to each other with a chiral smectic liquid crystal held therebetween, and whose opposing surfaces are each provided with electrodes for applying a voltage to the chiral smectic liquid crystal. A chiral smectic liquid crystal in an aligned state, the chiral smectic liquid crystal exhibiting at least two optically stable states, wherein at least one of the pair of counter electrodes is made of amorphous ITO whose surface is flattened.
A chiral smectic liquid crystal device having an LB film having a film thickness of 5 nm or less on the electrode.

The above-mentioned first liquid crystal element of the present invention is further characterized in that "at least one of the pair of counter electrodes is not subjected to uniaxial alignment treatment", "the chiral smectic liquid crystal is fluorocarbon terminated. A chiral smectic liquid crystal composition comprising a fluorine-containing liquid crystalline compound having a smectic mesophase or a latent smectic mesophase, the chain comprising a chain and a hydrocarbon end chain, the both end chains being bound by a central nucleus.
That the chiral smectic liquid crystal composition containing the fluorine-containing compound contains one or more compounds represented by the following general formula (I), P-Q-A-W-B- (T-D) _n -U-V (I) (In the formula, A, B and D each represent the same or different aromatic ring, heteroaromatic ring, aliphatic ring or their condensed ring structure. These rings are substituted. Maybe, Q,
W and T are each the same or different single bond, -O
-, -COO-, -OCO-, -C≡C-, -CONR
-, - NRCO -, - NR -, - CH 2 -, - CH = N
-, -N = CH-, -CH = CH-, -COS-, -S
_{CO -, - CH 2 CH 2} -, - CH 2 O -, - OCH 2
Represents-. R represents an alkyl group. P represents an alkyl group which may be substituted. n represents 0, 1 or 2. U _{is, -CO-C m H 2m -} , - O-C m H 2m -, -
_{C m H 2m -CO -, -} C m H 2m -O -, - C m H 2m -,
_{-OSO 2 -, - SO 2 O} -, - SO 2 -, - SO 2 -
_{C m H 2m -, - O} -C m H 2m -O-C m H 2m -, - C m
_{H 2m -SO 2 -, - C} m H 2m -O-C m H 2m -O -, -
_{C m H 2m -N (C m} 'H 2m' + 1) -SO 2 -, - C m H 2m
_{-N (C m 'H 2m'} + 1) -CO -, - SO 2 -N (C m 'H
_{2m '+ 1) -C m H} 2m -, - CO-N (C m' H 2m '+ 1) -
Represents C _m H _2m −, and m and m ′ each represent the same or different integers from 1 to 20. V _is- (C _p F _2p
O) _q C _r F _{2r + 1} . When q is plural, p is an integer of 1 to 10 independently for each (C _p F _2p O), and when q is 1, it is an integer of 1 to 10. q is an integer of 1 to 6. r is an integer of 1 to 10. ) "The chiral smectic liquid crystal is a liquid crystal having no cholesteric phase".

The second aspect of the present invention is to provide a pair of substrates which are opposed to each other with a chiral smectic liquid crystal held therebetween and whose opposing surfaces are provided with electrodes for applying a voltage to the chiral smectic liquid crystal. A method for manufacturing a chiral smectic liquid crystal device, in which the chiral smectic liquid crystal in an aligned state exhibits at least two optically stable states, wherein at least one electrode of the pair of opposing electrodes is surface-planarized amorphous ITO.
And a LB film having a film thickness of 5 nm or less formed on the electrode, and a method of manufacturing a chiral smectic liquid crystal element.

The present invention is particularly effective in obtaining a uniform alignment of a chiral smectic liquid crystal having no Ch phase, but can improve the alignment uniformity even in a chiral smectic liquid crystal having a Ch phase. Is.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION An example of the chiral smectic liquid crystal element of the present invention (a structural example of a liquid crystal cell) will be described with reference to FIG.

In FIG. 1, 11a and 11b are glass substrates,
12a and b are transparent electrodes, and 14a and b are alignment films. Short-circuit prevention layers 13a and 13b may be provided between the alignment films 14a and 14b and the transparent electrodes 12a and 12b. These substrates 11a and 11b are bead spacers 16 such as silica beads.
A cell is created by pasting together with a sealing agent (not shown) through the. The chiral smectic liquid crystal 15 is injected into this cell by utilizing the capillary phenomenon or the like to form a chiral smectic liquid crystal element. In addition, 17a,
b is a polarizing plate.

At least one of the transparent electrodes 12a and 12b is made of a thin film of amorphous ITO. Amorphous ITO can be obtained by setting the substrate temperature to about 50 ° C. when forming a film by sputtering.
The average surface roughness is 2n
It can be controlled to m or less.

Specific examples of the compound represented by the general formula (I) in the chiral smectic liquid crystal composition preferably used in the present invention include the following. The chiral smectic liquid crystal composition used in the present invention may be composed of only the above-mentioned fluorine-containing liquid crystalline compound or a mixture with a non-fluorine-containing compound.

[0020]

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[0021]

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[0022]

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[0023]

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[0024]

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[0025]

[Chemical 6]

[0026]

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[0027]

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[0028]

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[0029]

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[0030]

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[0031]

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Specific examples of compounds having a chiral moiety include the following.

[0033]

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[0034]

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[0035]

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[0036]

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[0037]

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[0038]

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[0039]

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[0040]

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[0041]

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These compounds are used alone or in the form of a mixture of plural compounds as a base material of the chiral smectic liquid crystal composition.

For the chiral smectic liquid crystal composition used in the present invention, various other liquid crystal compounds including a chiral compound and an achiral compound other than the above are appropriately selected according to the compatibility of the compounds, the control of the layer spacing and the like. In addition, additives such as antioxidants, ultraviolet absorbers, dyes and pigments may be contained.

Next, a method of forming the horizontal alignment film on the transparent electrode made of amorphous ITO whose surface is flattened as described above by using the LB method will be described. 2 is LB
1 is a schematic diagram of a film accumulator. The water tank 1 is filled with pure water 2, and an amphipathic polyimide precursor obtained by reacting, for example, a polyamic acid with a long-chain alkylamine is spread on the still water surface to form a film 4 on the water surface. Then, the barrier 3 is moved in the direction of arrow A to compress the film 4 on the water surface. At this time, the cumulative surface pressure of the membrane 4 on the water surface is kept at a constant value. When the substrate 5 is moved up and down at a constant cumulative speed while keeping the cumulative surface pressure constant, the film on the still water surface is transferred onto the substrate. By repeating this several times, a plurality of LB films are formed on the transparent electrode. A polyimide alignment film is obtained by heat-treating this LB film.

In the present invention, the alignment film is formed with a film thickness of 5 nm or less. As a result, the capacity of the alignment film is increased, and it is possible to achieve a predetermined display characteristic in which bistability is maintained without causing an afterimage and a switching failure. Furthermore, since the transparent electrode made of amorphous ITO on which the alignment film is formed is sufficiently flattened (for example, the average surface roughness is 2 nm or less), the alignment state of the liquid crystal is 5 Is not affected by the irregularities on the surface of the transparent electrode, and is capable of imparting sufficiently uniform uniaxial orientation to a chiral smectic liquid crystal having no Ch phase.
In addition, even in a chiral smectic liquid crystal having a Ch phase, alignment uniformity can be improved.

[0046]

EXAMPLES The present invention will be described in detail below with reference to examples.

[Example] A pair of glass substrates on which surface-flattened amorphous ITO having a film thickness of 70 nm was formed were prepared as transparent electrodes. The average surface roughness of this transparent electrode is about 2 nm.

As a hydrophobic treatment for enhancing the adsorptivity of the LB film, ODA (octadecylamine) was further formed on the transparent electrode of one substrate by the LB method.

Next, polyamic acid LP64 (manufactured by Toray Industries, Inc.), which is a polyimide precursor, was prepared in NMP (N-methylpyrrolidone) to a concentration of 1 mM. Further, dimethylhexadecylamine was prepared in NMP so as to be 2 mM, and mixed in an equal amount with the LP64 solution to obtain an amphiphilic polyimide precursor. This precursor was spread on the still water surface of the LB film forming apparatus, and several layers were formed on the amorphous ITO electrode substrate by the LB method under the conditions of a cumulative surface pressure of 35 mN / m and a cumulative speed of 6.75 mm / min. Filmed After forming the LB film, imidization is performed for 30 minutes in an oven at 300 ° C. to obtain a polyimide horizontal alignment film.

An IPA (isopropyl alcohol) solution in which 0.01% by weight of silica beads having an average particle size of 2.0 μm are dispersed on the surface of the substrate on which the horizontal polyimide alignment film has been formed as described above is 1500 rpm for 10 seconds. Spin coating was performed under the conditions, and bead spacers having a dispersion density of about 100 / mm ² were scattered.

On the transparent electrode of the other substrate, 0.5% by weight of a silane coupling agent ODSE (manufactured by Chisso Corporation) was used.
The solvent diluted with ethanol was spin-coated at 2000 rpm for 20 seconds, and tentatively dried at 90 ° C. for 5 minutes.
Dry at 0 ° C. for 1 hour. Thereafter, a thermosetting liquid adhesive was applied by a printing method.

The two substrates thus obtained were laminated facing each other and heat-cured in an oven at 150 ° C. for 90 minutes to obtain a cell.

The following chiral smectic liquid crystal composition A was placed in the cell under reduced pressure (10 Pa) and isotropic phase temperature (100
C.) and slowly cooled to a chiral smectic phase to obtain a chiral smectic liquid crystal device.

[0054]

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The composition (weight ratio; compound a / b / c / d)
/E=46.4/15.5/30.9/5.2/2.
The physical property parameters of 0) are shown below.

[0056]

(Equation 1)

Tilt angle (10 ° C.) Θ = 27.2 ° Spontaneous polarization (10 ° C.) Ps = -45.9 (nC / cm)
² )

The chiral smectic liquid crystal device of this example was placed on the FP82 hot stage controlled by the FP80HT temperature controller manufactured by METTLER CORPORATION, and the phase transition from the isotropic phase to the SmA phase was performed. The orientation state at this time is shown in FIG.

As shown in FIG. 3, in this embodiment, Ch
It was possible to obtain a uniform alignment with respect to the isotropic phase (Iso) -smectic A phase (SmA) -chiral smectic liquid crystal having no phase.

[Comparative Example] A cell was prepared in the same manner as in the above example except that a thin film of ITO having a thickness of 150 nm was used as the transparent electrode on the side where the horizontal alignment film was formed by the LB method. At this time, the average surface roughness on the transparent electrode was about 5 nm. The alignment state of this comparative example is shown in FIG.

As shown in FIG. 4, since the influence of surface irregularities on the alignment of the liquid crystal is large, a random alignment state was obtained.

[0062]

As described above, according to the chiral smectic liquid crystal element of the present invention, it is possible to uniformly align the chiral smectic liquid crystal having no Ch phase.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an example of a chiral smectic liquid crystal device of the present invention.

FIG. 2 is a schematic view of an LB film accumulating device.

FIG. 3 is a diagram showing an alignment state of a chiral smectic liquid crystal element according to an example of the present invention.

FIG. 4 is a diagram showing an alignment state of a chiral smectic liquid crystal element according to a comparative example.

[Explanation of symbols]

 1 Water Tank 2 Pure Water 3 Barrier 4 Film 5 Substrate 11a, b Glass Substrate 12a, b Transparent Electrode 13a, b Shorting Preventing Film 14a, b Alignment Film 15 Chiral Smectic Liquid Crystal 16 Bead Spacer 17a, b Polarizing Plate

Front page continued (72) Inventor Masanobu Asaoka 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Yasuaki Takeda 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Ikuo Nakazawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Yasushi Asao 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (6)

[Claims] 1. A chiral smectic in an aligned state, which is provided with a pair of substrates which are opposed to each other with a chiral smectic liquid crystal held therebetween and whose opposing surfaces are respectively formed with electrodes for applying a voltage to the chiral smectic liquid crystal. A chiral smectic liquid crystal device in which liquid crystal exhibits at least two optically stable states, and at least one electrode of the pair of counter electrodes has a surface-flattened amorphous ITO (Indium Tin).
A chiral smectic liquid crystal element comprising an LB film having a thickness of 5 nm or less on the electrode. 2. The chiral smectic liquid crystal device according to claim 1, wherein at least one of the pair of counter electrodes is not subjected to uniaxial alignment treatment. 3. A fluorine-containing liquid crystalline compound comprising a fluorocarbon terminal chain and a hydrocarbon terminal chain, the both terminal chains being bound by a central nucleus, and having a smectic mesophase or a latent smectic mesophase. The chiral smectic liquid crystal element according to claim 1 or 2, which is a chiral smectic liquid crystal composition containing the same. 4. The chiral smectic liquid crystal device according to claim 3, wherein the chiral smectic liquid crystal composition containing the fluorine-containing compound contains one or more compounds represented by the following general formula (I). . P-Q-A-W-B- (T-D) _n- U-V (I) (In the formula, A, B, and D are the same or different aromatic rings, heteroaromatic rings, and aliphatic rings. Alternatively, they represent a condensed ring structure thereof, which ring may be substituted.
W and T are each the same or different single bond, -O
-, -COO-, -OCO-, -C≡C-, -CONR
-, - NRCO -, - NR -, - CH 2 -, - CH = N
-, -N = CH-, -CH = CH-, -COS-, -S
_{CO -, - CH 2 CH 2} -, - CH 2 O -, - OCH 2
Represents-. R represents an alkyl group. P represents an alkyl group which may be substituted. n represents 0, 1 or 2. U _{is, -CO-C m H 2m -} , - O-C m H 2m -, -
_{C m H 2m -CO -, -} C m H 2m -O -, - C m H 2m -,
_{-OSO 2 -, - SO 2 O} -, - SO 2 -, - SO 2 -
_{C m H 2m -, - O} -C m H 2m -O-C m H 2m -, - C m
_{H 2m -SO 2 -, - C} m H 2m -O-C m H 2m -O -, -
_{C m H 2m -N (C m} 'H 2m' + 1) -SO 2 -, - C m H 2m
_{-N (C m 'H 2m'} + 1) -CO -, - SO 2 -N (C m 'H
_{2m '+ 1) -C m H} 2m -, - CO-N (C m' H 2m '+ 1) -
Represents C _m H _2m −, and m and m ′ each represent the same or different integers from 1 to 20. V _is- (C _p F _2p
O) _q C _r F _{2r + 1} . When q is plural, p is an integer of 1 to 10 independently for each (C _p F _2p O), and when q is 1, it is an integer of 1 to 10. q is an integer of 1 to 6. r is an integer of 1 to 10. ) 5. The chiral smectic liquid crystal device according to claim 1, wherein the chiral smectic liquid crystal is a liquid crystal having no cholesteric phase. 6. A chiral smectic in an aligned state is provided with a pair of substrates, which are opposed to each other with a chiral smectic liquid crystal held therebetween, and whose opposing surfaces respectively have electrodes for applying a voltage to the chiral smectic liquid crystal. A method for manufacturing a chiral smectic liquid crystal device in which liquid crystal exhibits at least two optically stable states, wherein at least one electrode of the pair of counter electrodes is made into an amorphous ITO (Indium Tin).
Oxide), and a step of forming an LB film having a film thickness of 5 nm or less on the electrode, the method of manufacturing a chiral smectic liquid crystal element.